1. Field of the Invention
This invention relates to musical tone synthesis and in particular is concerned with an improvement for producing several tone variations from stored musical waveforms.
2. Description of the Prior Art
The most obvious method to imitate an acoustic musical instrument is to record the sound and to replay the recording in response to an actuated keyswitch on an array of keyswitches. While at first thought the straightforward technique of recording and keyed playback seems to be attractive, a practical realization of such a musical instrument can be burdened by a large amount of memory required to store the recorded data. The maximum amount of memory is associated with a tone generation system that uses a separate and distinct recording for each note played in the range of the musical instrument's keyboard. Some economy in the memory requirement has been made by using a single recording for several contiguous musical notes. This economy is based upon the tacit assumption that the waveshape for the imitated acoustic musical instrument does not change markedly between several contiguous successive notes.
Electronic musical tone generators that operate by playing back recorded musical waveshapes stored in a binary digital data format have been given the generic name of PCM (Pulse Code Modulation). A musical instrument of the PCM type is described in U.S. Pat. No. 4,383,462 entitled "Electronic Musical Instrument." In the system described in the patent, the complete waveshape of a musical tone is stored for the attack and decay portions of the musical tone. A second memory is used to store the remainder of the tone which comprises the release phase of the musical tone. The sustain phase of the musical tone is obtained by using a third memory which stores only points for a single period of a waveshape. After the end of the decay phase, the data stored in the third memory is read out repetitively and the output data is multiplied by an envelope function generator to create the amplitude variation for the sustain and release portions of the generated musical tone.
Because of the large amount of memory required for a stored waveform PCM musical tone generation system, it is desirable to employ techniques which use a single stored waveform to generate more than one musical tone. It is an object of the present invention to produce several different musical tones from a single stored waveshape.